The instant invention relates to coating compositions comprising carbamate functional polymers and reactive additives. In particular, the invention provides coating compositions comprising a reactive additive comprising at least one compound having a molecular weight of from 131 to 2000 and at least one primary carbamate group and at least one alkyl group selected from the group consisting of straight chain alkyl groups of more than 10 carbons, branched alkyl group of from 5 to 30 carbons, and mixtures thereof.
Curable coating compositions such as thermoset coatings are widely used in the coatings art. They are often used for topcoats in the automotive and industrial coatings industry. Color-plus-clear composite coatings are particularly useful as topcoats where exceptional gloss, depth of color, distinctness of image, or special metallic effects is desired. The automotive industry has made extensive use of these coatings for automotive body panels. Color-plus-clear composite coatings, however, require an extremely high degree of clarity in the clearcoat to achieve the desired visual effect. High-gloss coatings also require a low degree of visual aberrations at the surface of the coating in order to achieve the desired visual effect such as high distinctness of image (DOI).
As such, these coatings are especially susceptible to a phenomenon known as environmental etch. Environmental etch manifests itself as spots or marks on or in the finish of the coating that often cannot be rubbed out.
It is often difficult to predict the degree of resistance to environmental etch that a high gloss or color-plus-clear composite coating will exhibit. Many coating compositions known for their durability and/or weatherability when used in exterior paints, such as high-solids enamels, do not provide the desired level of resistance to environmental etch when used in high gloss coatings such as the clearcoat of a color-plus-clear composite coating.
Many compositions have been proposed for use as the clearcoat of a color-plus-clear composite coating, such as polyurethanes, acid-epoxy systems and the like. However, many prior art systems suffer from disadvantages such as coatability problems, compatibility problems with the pigmented basecoat, solubility problems. Moreover, very few one-pack coating compositions have been found that provide satisfactory resistance to environmental etch, especially in the demanding environment of automotive coatings.
There is also a continuing desire to reduce the volatile organic content (VOC) of coating compositions. This must be done without sacrificing the Theological properties of the coating composition required for trouble-free application of the composition while maintaining the desired level of appearance. In addition, it is desirable to provide coatings with a good combination of properties such as durability, hardness, flexibility, and resistance to scratching, marring, solvents, and acids.
Curable coating compositions utilizing carbamate-functional resins are described in U.S. Pat. No. 5,356,669. These coating compositions can provide significant etch advantages over other coating compositions, such as hydroxy-functional acrylic/melamine coating compositions. It may often be desirable, however, to provide still further improvements in the above described coating properties.
U.S. Pat. No. 4,814,382, 5,114,015, and 5,158,808 describe the use of certain N-alkyl carbamate compounds as reactive diluents in coating compositions having OH-functional curable polymer resins. These compounds, however, may require excessively high catalyst or temperature levels in order to fully react into the crosslink matrix during cure of the film.
WO 87/00851 describes the use of certain reactive carbamate derivatives in an effort to minimize the emission of volatile organic compounds (VOC). U.S. Pat. No. 5,744,550 describes the use of primary carbamate additives. However, further reductions in VOC are desirable without loss of desirable performance properties such as etch resistance and the like.
It has been surprisingly discovered that certain primary carbamate reactive additives provide advantages over the prior art. In particular, it has been found that the incorporation of a particular reactive additive provides improved sprayability at a given nonvolatile level and advantageous resistance to environmental etch, even with respect to compositions containing carbamate functional polymers. The reactive additive comprises at least one compound having a molecular weight of from 131 to 2000 and comprising at least one primary carbamate group and at least one alkyl group selected from the group consisting of straight chain alkyl groups of more than 10 carbons, branched alkyl groups of from 5 to 30 carbons, and mixtures thereof.
The invention thus provides a curable coating composition comprising (A) a polymer resin comprising at least one primary carbamate group, (B) a curing agent having groups that are reactive with said carbamate groups on (A), and (C) a reactive additive comprising at least one compound having a molecular weight of from 131 to 2000 and comprising at least one primary carbamate group and at least one alkyl group selected from the group consisting of straight chain alkyl groups of more than 10 carbons, branched alkyl groups of from 5 to 30 carbons, and mixtures thereof, wherein one or both of (A) and (B) comprise groups that are reactive with the primary carbamate group of (C).
The polymer component (A) used in the composition of the invention can be prepared in a variety of ways. One way to prepare such polymers is to prepare an acrylic monomer having carbamate functionality in the ester portion of the monomer. Such monomers are well known in the art and are described, for example in U.S. Pat. No. 3,479,328, 3,674,838, 4,126,747, 4,279,833, and 4,340,497, 5,356,669, and WO 94/10211, the disclosures of which are incorporated herein by reference. One method of synthesis involves reaction of a hydroxy ester with urea to form the carbamyloxy carboxylate (i.e., carbamate-modified acrylic). Another method of synthesis reacts an xcex1,xcex2-unsaturated acid ester with a hydroxy carbamate ester to form the carbamyloxy carboxylate. Yet another technique involves formation of a hydroxyalkyl carbamate by reacting a primary or secondary amine or diamine with a cyclic carbonate such as ethylene carbonate. The hydroxyl group on the hydroxyalkyl carbamate is then esterified by reaction with acrylic or methacrylic acid to form the monomer. Other methods of preparing carbamate-modified acrylic monomers are described in the art, and can be utilized as well. The acrylic monomer can then be polymerized along with other ethylenically unsaturated monomers, if desired, by techniques well known in the art.
An alternative route for preparing the polymer (A) used in the composition of the invention is to react an already-formed polymer such as an acrylic polymer with another component to form a carbamate-functional group appended to the polymer backbone, as described in U.S. Pat. No. 4,758,632, the disclosure of which is incorporated herein by reference. One technique for preparing polymers useful as component (A) involves thermally decomposing urea (to give off ammonia and HNCO) in the presence of a hydroxy-functional acrylic polymer to form a carbamate-functional acrylic polymer. Another technique involves reacting the hydroxyl group of a hydroxyalkyl carbamate with the isocyanate group of an isocyanate-functional acrylic or vinyl monomer to form the carbamate-functional acrylic. Isocyanate-functional acrylics are known in the art and are described, for example in U.S. Pat. No. 4,301,257, the disclosure of which is incorporated herein by reference. Isocyanate vinyl monomers are well known in the art and include unsaturated m-tetramethyl xylene isocyanate (sold by American Cyanamid as TMI(copyright)). Yet another technique is to react the cyclic carbonate group on a cyclic carbonate-functional acrylic with ammonia in order to form the carbamate-functional acrylic. Cyclic carbonate-functional acrylic polymers are known in the art and are described, for example, in U.S. Pat. No. 2,979,514, the disclosure of which is incorporated herein by reference. Another technique is to transcarbamylate a hydroxy-functional acrylic polymer with an alkyl carbamate. A more difficult, but feasible way of preparing the polymer would be to trans-esterify an acrylate polymer with a hydroxyalkyl carbamate.
The polymer (A) will generally have a molecular weight of 2000-20,000, and preferably from 3000-6000. As used herein, molecular weight means number average molecular weight, and can be determined by the GPC method using a polystyrene standard. The carbamate content of the polymer, on a molecular weight per equivalent of carbamate functionality, will generally be between 200 and 1500, and preferably between 300 and 500. The glass transition temperature, Tg, of components (A) and (B) can be adjusted to achieve a cured coating having the Tg for the particular application involved.
The polymer component (A) can be represented by the randomly repeating units according to the following formula: 
In the above formula, R1 represents H or CH3. R2 represents H, alkyl, preferably of 1 to 6 carbon atoms, or cycloalkyl, preferably up to 6 ring carbon atoms. It is to be understood that the terms alkyl and cycloalkyl are to include substituted alkyl and cycloalkyl, such as halogen-substituted alkyl or cycloalkyl. Substituents that will have an adverse impact on the properties of the cured material, however, are to be avoided. For example, ether linkages are thought to be susceptible to hydrolysis, and should be avoided in locations that would place the ether linkage in the crosslink matrix. The values x and y represent weight percentages, with x being 10 to 90% and preferably 40 to 60%, and y being 90 to 10% and preferably 60 to 40%.
In the formula, A represents repeat units derived from one or more ethylenically unsaturated monomers. Such monomers for copolymerization with acrylic monomers are known in the art. They include alkyl esters of acrylic or methacrylic acid, e.g., ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, butyl methacrylate, isodecyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and the like; and vinyl monomers such as unsaturated m-tetramethyl xylene isocyanate (sold by American Cyanamid as TMI(copyright)), styrene, vinyl toluene and the like.
L represents a divalent linking group, preferably an aliphatic of 1 to 8 carbon atoms, cycloaliphatic, or aromatic linking group of 6 to 10 carbon atoms. Examples of L include 
xe2x80x94(CH2)xe2x80x94,xe2x80x94(CH2)2xe2x80x94,xe2x80x94(CH2)4xe2x80x94, and the like. In one preferred embodiment, xe2x80x94Lxe2x80x94 is represented by xe2x80x94COOxe2x80x94Lxe2x80x2xe2x80x94 where Lxe2x80x2 is a divalent linking group. Thus, in a preferred embodiment of the invention, the polymer component (a) is represented by randomly repeating units according to the following formula: 
In this formula, R1, R2, A, x, and y are as defined above. Lxe2x80x2 may be a divalent aliphatic linking group, preferably of 1 to 8 carbon atoms, e.g., xe2x80x94(CH2)xe2x80x94, xe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)4xe2x80x94, and the like, or a divalent cycloaliphatic linking group, preferably up to 8 carbon atoms, e.g., cyclohexyl, and the like. However, other divalent linking groups can be used, depending on the technique used to prepare the polymer. For example, if a hydroxyalkyl carbamate is adducted onto an isocyanate-functional acrylic polymer, the linking group Lxe2x80x2 would include an xe2x80x94NHCOOxe2x80x94 urethane linkage as a residue of the isocyanate group.
Alternatively, as indicated in the Example below, a suitable polymer resin is the reaction product of the isocyanurate of IPDI (isophorone diisocyante) and a beta-hydroxy alkyl carbamate such as beta-hydroxybutyl carbamate.
The composition of the invention is cured by a reaction of the carbamate-functional polymer component (A) with a component (B) that Is a compound having a plurality of functional groups that are reactive with the carbamate groups on component (A). Such reactive groups include active methylol or methylalkoxy groups on aminoplast crosslinking agents or on other compounds such as phenoyformaldehyde adducts, siloxane groups, and anhydride groups. Examples of (B) compounds include melamine formaldehyde resin (including monomeric or polymeric melamine resin and partially or fully alkylated melamine resin), blocked or unblocked polyisocyanates (e.g., TDI, MDI, isophorone diisocyanate, hexamethylene diisocyanate, and isocyanurate trimers of these, which may be blocked for example with alcohols or oximes), urea resins (e.g., methylol ureas such as urea formaldehyde resin, alkoxy ureas such as butylated urea formaldehyde resin), polyanhydrides (e.g., polysuccinic anhydride), and polysiloxanes (e.g., trimethoxy siloxane). Aminoplast resin such as melamine formaldehyde resin or urea formaldehyde resin are especially preferred.
Compounds suitable for use as reactive additive (C) are those having at least one primary carbamate group and at least one alkyl radical selected from the group consisting of straight chain alkyl groups of more than 10 carbons, branched alkyl groups of from 5 to 30 carbons, and mixtures thereof.
As used herein, xe2x80x9cprimary carbamate groupxe2x80x9d refers to the functional group having the structure 
Thus, the primary carbamate group of the invention may be defined as a terminal or pendent carbamate group. Although compounds suitable for use as reactive additive (C) may comprise more than one primary carbamate group, it is most preferred that such compounds have one primary carbamate group.
In addition to the at least one primary carbamate group, compounds suitable for use as reactive additive (C) will further comprise at least one alkyl group selected from the group consisting of branched alkyl groups having from 5 to 30 total carbons, straight chain alkyl groups of more than 10 carbons, and mixtures thereof.
As used herein, the term xe2x80x9cbranchedxe2x80x9d refers to both lateral branches and forked branches. Lateral refers to a branch of two small chains at the end atom of a carbon chain. Forked refers to a branch of two small chains in the middle of a carbon chain. For the purposes of the instant invention a carbon chain may be from 1 to 15 carbons, more preferably from 1 to 8 and most preferably from 1 to 3. The total number of carbon atoms in the branched alkyl group is obtained by adding the total number of carbons in the main carbon chain+the number of carbons in all alkyl chains extending from the main carbon chain.
It will be appreciated that the main carbon chain may be from 1 to 25 carbons, preferably from 1 to 10, most preferably from 1 to 4. Most preferably, the main chain will be an aliphatic carbon chain free of unsaturation. Although the at least one branched alkyl group may comprise from 5 to 30 total carbons, more preferably, it will have from 5 to 15 carbons and most preferably from 8 to 12 carbons.
Finally, it will be appreciated that suitable xe2x80x9cat least one alkyl groupsxe2x80x9d for use in reactive additive (C) will be substantially free of functional groups that are reactive with one or more of components (A) and (B). Thus, the at least one alkyl group selected from the group consisting of branched alkyl groups having from 5 to 30 total carbons, straight chain alkyl groups of more than 10 carbons, and mixtures thereof, will be free of hydroxyl groups and the like.
An example of an especially suitable at least one branched alkyl group is 
wherein R1, R2, and R3 are alkyl groups of from 1 to 10 carbons each, preferably aliphatic groups of from 1 to 10 carbons. Most preferably, R1, R2, and R3 will total from 8 to 12 carbons with at least one of R1, R2, and R3 being a methyl group.
In another suitable branched alkyl group of the above same structure, one of R1, R2, and R3, may be hydrogen, with the other two substituent groups being alkyl groups of from 1-10 carbons, preferably aliphatic groups of from 1 to 10. An example of such a group is 
In this instance, the above structure is understood to be an example of lateral branching.
In a particularly preferred embodiment, the at least one branched alkyl group will comprise 
wherein x+y=5.
Alternatively, the compound suitable for use as reactive additive (C) may include a straight chain alkyl group of more than 10 carbons, preferably more than 15 carbons and most preferably more than 18. Examples of suitable straight chain, aliphatic alkyl groups include 1-eicosanyl, 1-octadecyl, 1-arachidyl, 1-dodecyl, 1-decyl, and 1-octyl, and the like.
It is most preferred that compounds suitable for use as reactive additive (C) include at least one group which is a branched alkyl group such as described above.
Compounds suitable for use as reactive additive (C) may further include heteratoms such as O and N, most preferably O. Such heteratoms may be incorporated in the form of groups such as esters, hydroxyls, ether, carboxyls, mixtures thereof and the like. Preferred are esters, hydroxyls, and mixtures thereof. Most preferably, a compound will comprise at least one hydroxyl group and one ester group in addition to the carbamate functional group and the at least one alkyl group.
Particularly suitable compounds for use as reactive additive (C) are those having the formula: 
wherein X is a branched alkyl radical of from 5 to 30 total carbons, more preferably from 5 to 15 total carbons and most preferably from 8 to 12 total carbons.
A more preferred compound for use as reactive additive (C) is that having the formula: 
wherein R1, R2, and R3 are each alkyl groups of from 1 to 10 carbons, especially compounds wherein R1, R2, and R3 total from 8 to 12 carbons with at least one of R1, R2, and R3 being a methyl group.
The most preferred compound for use as reactive additive (C) is that having the formula: 
wherein R2 and R3 are respectively xe2x80x94(CH2)xCH3 and xe2x80x94(CH2)yCH3 wherein x+y=5.
The invention further provides a method of making the reactive additive of the invention. It has been discovered that the most preferred reactive additive of the invention can be made by providing a compound having at least one epoxy group and at least one alkyl group selected from the group consisting of branched alkyl groups of from 5 to 30 total carbons, straight chain alkyl groups of more than 10 carbons, and mixtures thereof. It is preferred that the compound provided will comprise at lest one branched alkyl group of from 5 to 30 total carbons. More preferably the epoxy functional compound will have one epoxy group and a branched alkyl group of from 5 to 15 total carbons and most preferably from 8 to 12 total carbons.
Examples of preferred epoxy functional/branched alkyl group containing compounds are glycidyl ethers, glycidyl esters, and epoxies based on alpha olefins, 2-ethyl hexyl glycidyl ether, and glycidyl esters of the formula: 
wherein X is a branched alkyl hydrocarbon radical containing from about 5 to 30 total carbons. More preferably, X is a tertiary aliphatic group of from about 5 to 15 carbons and most preferably from 8 to 12 carbons, such as neopentanoate, neoheptanoate, and neodecanoate. Glycidyl esters of commercially available mixtures of tertiary aliphatic carboxylic acids such as those available from Shell Chemical Company as VERSATIC ACID 911 are particularly preferred as the epoxy group and branched alkyl group containing compound. The glycidyl esters are commercially available from Shell Chemical Company as CARDURA E or GLYDEXX N-10 from Exxon Chemical Company.
The epoxy group and branched alkyl group containing compound is then reacted with carbon dioxide so as to produce a carbonate functional compound. A ring opening catalyst such as triphenyl phosphene or tertiary ammonium salt is normally employed. While the reaction will go under atmospheric pressure, positive pressures are usually used to reduce reaction time.
The resulting carbonate functional compound is subsequently reacted with ammonia or ammonium hydroxide to provide a the primary oarbamate functional reactive additive of the invention.
Alternatively, rather than produce a carbonate functional compound, the epoxy could be reacted with water to form alcohols, with subsequent conversion of the alcohols into carbamates via transesterification, urea decomposition and the like.
In a second method of the invention, glycol diols having the same structures of the epoxy functional compounds listed above can be used as a starting material. Such glycol diols must have at least one alkyl group selected from the group consisting of branched alkyl groups of from 5 to 30 total carbons, straight chain alkyl groups of more than 10 carbons, and mixtures thereof. Glycol diol as used herein refers to a diol wherein the two hydroxy groups are on adjacent carbons. Suitable glycol diols may contain other heteroatom groups as discussed above.
The glycol diols are reacted with phosgene or similar materials such as triphosgene. The resulting cyclic carbonate is then reacted as described above to form the primary carbamate functional reactive additive.
Finally, the glycol diols can be directly converted into primary carbamates using techniques such as reaction with urea, HNCO gas, or transesterification with carbamate ester such as methyl carbamate.
The compound (C) will generally have a molecular weight of 131-2000, and preferably from 131-1000 and most preferably from 131 to 500. The glass transition temperature, Tg, of components (A), (B), and (C) cap be adjusted to achieve a cured coating having the desired Tg for the particular application involved. The compound (C) is preferably used at levels between 3 to 50 percent (based on total resin solids of the coating composition), and more preferably between 5 to 25 percent.
According to the present invention, at least one of components (A) and (B), or both components (A) and (B) must have at least one group thereon that is reactive with the carbamate group(s) on component (C). This is preferably accomplished through the selection of an aminoplast as component (B). Depending on the cure conditions, other compounds identified above as component (13) may also be reactive with the carbamate group(s) on component (C). Component (A) may also contain groups that are reactive with carbamate, such as an acrylic polymer containing isobutoxymethyl acrylamide groups.
A solvent may optionally be utilized in the coating composition used in the practice of the present invention. Although the composition used according to the present invention may be utilized, for example, in the form of substantially solid powder, or a dispersion, it is often desirable that the composition is in a substantially liquid state, which can be accomplished with the use of a solvent. This solvent should act as a solvent with respect to both the carbamate-functional compound (A) as well as the component (B). In general, depending on the solubility characteristics of components (A) and (B), the solvent can be any organic solvent and/or water. In one preferred embodiment, the solvent is a polar organic solvent. More preferably, the solvent is a polar aliphatic solvents or polar aromatic solvents. Still more preferably, the solvent is a ketone, ester, acetate, aprotic amide, aprotic sulfoxide, or aprotic amine. Examples of useful solvents include methyl ethyl ketone, methyl isobutyl ketone, m-amyl acetate, ethylene glycol butyl ether-acetate, propylene glycol monomethyl ether acetate, xylene, N-methylpyrrolidone, or blends of aromatic hydrocarbons. In another preferred embodiment, the solvent is water or a mixture of water with small amounts of co-solvents.
The coating composition used in the practice of the invention may include a catalyst to enhance the cure reaction. For example, when aminoplast compounds, especially monomeric melamines, are used as component (B), a strong acid catalyst may be utilized to enhance the cure reaction. Such catalysts are well known in the art and include, for example, p-toluenesulfonic acid, dinonylnaphthalene disulfonic acid, dodecylbenzenesulfonic acid, phenyl acid phosphate, monobutyl maleate, butyl phosphate, and hydroxy phosphate ester. Strong acid catalysts are often blocked, e.g. with an amine. Other catalysts that may be useful in the composition of the invention include Lewis acids, zinc salts, and tin salts.
In a preferred embodiment of the invention, the solvent is present in the coating composition in an amount of from about 0.01 weight percent to about 99 weight percent, preferably from about 10 weight percent to about 60 weight percent, and more preferably from about 30 weight percent to about 50 weight percent.
Coating compositions can be coated on the article by any of a number of techniques well known in the art. These include, for example, spray coating, dip coating, roll coating, curtain coating, and the like. For automotive body panels, spray coating is preferred.
Any additional agent used, for example, surfactants, fillers, stabilizers, wetting agents, dispersing agents, adhesion promoters, UV absorbers, HALS, etc. may be incorporated into the coating composition. While the agents are well known in the prior art, the amount used must be controlled to avoid adversely affecting the coating characteristics.
The coating composition according to the invention is preferably utilized in a high-gloss coating and/or as the clearcoat of a composite color-plus-clear coating. High-gloss coatings as used herein are coatings having a 20xc2x0 gloss (ASTM D523-89) or a DOI (ASTM E430-91) of at least 80.
When the coating composition of the invention is used as a high-gloss pigmented paint coating, the pigment may be any organic or inorganic compounds or colored materials, fillers, metallic or other inorganic flake materials such as mica or aluminum flake, and other materials of kind that the art normally names as pigments. Pigments are usually used in the composition in an amount of 1% to 100%, based on the total solid weight of components A, B and C (i.e., a P:B ratio of 0.1 to 1).
When the coating composition according to the invention is used as the clearcoat of a composite color-plus-clear coating, the pigmented basecoat composition may any of a number of types well known in the art, and does not require explanation in detail herein. Polymers known in the art to be useful in basecoat compositions include acrylics, vinyls, polyurethanes, polycarbonates, polyesters, alkyds, and polysiloxanes. Preferred polymers include acrylics and polyurethanes. In one preferred embodiment of the invention, the basecoat composition also utilizes a carbamate-functional acrylic polymer. Basecoat polymers may be thermoplastic, but are preferably crosslinkable and comprise one or more type of cross-linkable functional groups. Such groups include, for example, hydroxy, isocyanate, amine, epoxy, acrylate, vinyl, silane, and acetoacetate groups. These groups may be masked or blocked in such a way so that they are unblocked and available for the cross-linking reaction under the desired curing conditions, generally elevated temperatures. Useful cross-linkable functional groups include hydroxy, epoxy, acid, anhydride, silane, and acetoacetate groups. Preferred cross-linkable functional groups include hydroxy functional groups and amino functional groups.
Basecoat polymers may be thermoplastic, self-cross-linkable, or may require a separate cross-linking agent that is reactive with the functional groups of the polymer. When the polymer comprises hydroxy functional groups, for example, the cross-linking agent may be an aminoplast resin, isocyanate and blocked isocyanates (including isocyanurates), and acid or anhydride functional cross-linking agents.
The coating compositions described herein are preferably subjected to conditions so as to cure the coating layers. Although various methods of curing may be used, heat curing is preferred. Generally, heat curing is effected by exposing the coated article to elevated temperatures provided primarily by radiative heat sources. Curing temperatures will vary depending on the particular blocking groups used in the cross-linking agents, however they generally range between 93xc2x0 C. and 177xc2x0 C. The compounds (C) according to the present invention are reactive even at relatively low cure temperatures. Thus, in a preferred embodiment, the cure temperature is preferably between 115xc2x0 C. and 150xc2x0 C., and more preferably at temperatures between 115xc2x0 C. and 138xc2x0 C. for a blocked acid catalyzed system. For an unblocked acid catalyzed system, the cure temperature is preferably between 82xc2x0 C. and 99xc2x0 C. The curing time will vary depending on the particular components used, and physical parameters such as the thickness of the layers, however, typical curing times range from 15 to 60 minutes, and preferably 15-25 minutes for blocked acid catalyzed systems and 10-20 minutes for unblocked acid catalyzed systems.